This is sort of an all purpose thread dealing with the unique issues facing things smaller or larger than human size can be in RPGs. However, I do have a specific issue I'd like to bring up.

How size tends to work in fiction fluctuates a lot, going from something that can make something invincible or simply a bigger target. In a lot of superhero fiction, giant characters aren't really that big a deal, while in other genres anything outside of human height is terrifying.

One particular disconnect I've seen between games and fiction is how smaller but powerful characters need to attack giant characters. In M&M, for instance, there's nothing really to stop Colossus from going up to Godzilla and just punching the Kaiju in the foot until the lizard fails a Toughness save by enough that it falls unconscious. In fiction, attacks to extremities against giant characters seem more to annoy them than anything, and you need to land a hit either on the central body mass or the head to inflict real injury to the creature.

For my own system, to simulate the advantage of longer weapons, I allow characters with longer limbs/weapons to take an "At Bay" option, where anyone with a shorter range trying to close in has to make an opposed check to get past their limbs to attack. Otherwise they can't advance, and if they fail bad enough, take damage. I think that's something giant characters would benefit from as well.

Another thing I'm thinking is that maybe attacks to extremities can only inflict some kind of condition to the limb, but you aren't really going to inflict lasting/potential KO damage to a creature unless you hit their torso or head. Attacking a leg might make it stumble, attacking an arm might make it drop something, but you need to land a good shot in the torso or head to really have an impact. Unless the attack is just powerful enough to sever limbs or some such.

Probably over-complicating a bit. Sometimes as fans/gamers, we have to step back and remember that rules mechanics are just gross simulations of reality-and in genre games, a gross simulation of fictional stories. In M&M terms, Growth gives bonuses to STA, and giant-sized character and monsters usually get high Protection scores as well, which is how the game does a "hard to bring down" effect. An in-game explanation for Colossus incapacitating Godzilla would be striking the limb with so much force it actually topples the King of Kaiju to his knees, and sends wracking pain to the beast's reptile brain.

(Real life example: a Thai kick-boxer can "knock out" opponents by landing a hard enough kick to a nerve cluster on a foe's thigh).

Games are never gong to reflect reality-or even "common sense"-in much detail. The games that try too hard are usually rules-dense and plodding when running combats.

I do understand what you're getting at-even if we got down to the human scale, which is pretty narrow in M&M terms (Jab had frequently mentioned there's little difference between any street-level/peak human set of stats). For example, pro-wrestling-"giants" like Paul Wight really aren't as strong as champion power lifers like Rusev or Big E of New Day, but height and weight means it's way easier for a very tall, heavy wrestler to body slam/suplex a smaller but stronger opponent than the reverse. The only real option is using/creating advantages or features, if you really want that level of accuracy.

Grey forgot to mention that there's Power Lifter's like Cesaro who can actually pick up dudes like Paul Wight,so you actual core body Strength would play a factor in this.

I use a Houserule for Giant stuff that might fit what your looking for Ares: Unless the Smaller person has a greater Strength than said Giant,they only get half-effects when attacking limbs.The Giant,however,can (depending on said Giant's size) do an Area of Effect attack on all enemies within arm reach.